Run Gazebo

These three steps will run Gazebo with a default world.

1. Install Gazebo.

2. Open a terminal. On most Ubuntu systems you can press CTRL+ALT+t

3. Start Gazebo by entering the following at the command prompt.

   gazebo
   
       
   

Run Gazebo with a robot

Let's simulate something a bit more interesting by loading a world with a pioneer2dx.

1. Open a terminal and enter the following command.

   gazebo worlds/pioneer2dx.world
   
       
   

Where are the worlds located?

You may have noticed the mysterious worlds/pioneer2dx.world argument in the above command. This instructs gazebo to find the pioneer2dx.world file, and load it on start.

World files are located in a versioned system directory, for example /usr/share/gazebo-7 on Ubuntu. If you have Gazebo 7.0 installed on Ubuntu, in a terminal type the following to see a complete list of worlds.

ls /usr/share/gazebo-7/worlds

  

For a Gazebo 7.0 installation on OS X using Homebrew, type the following to see a complete list of worlds.

ls /usr/local/share/gazebo-7/worlds

  

Client and server separation

The gazebo command actually runs two different executables for you. Thefirst is called gzserver, and the second gzclient.

The gzserver executable runs the physics update-loop and sensor datageneration. This is the core of Gazebo, and can be used independently of agraphical interface. You may see the phrase "run headless" thrown about inthe forums. This phrase equates to running only the gzserver. An exampleuse case would involve running gzserver on a cloud computer where a userinterface is not needed.

The gzclient executable runs a QT based userinterface. This application provides a nice visualization of simulation, andconvenient controls over various simulation properties.

Try running each of these executables. Open a terminal and run the server:

gzserver

  

Open another terminal and run the graphical client:

gzclient

  

At this point you should see the Gazebo user interface. You restart thegzclient application as often as you want, and even run multipleinterfaces.

This page describes each of the items involved in running a Gazebo simulation.

World Files

The world description file contains all the elements in a simulation, including robots, lights, sensors, and static objects. This file is formatted using SDF (Simulation Description Format), and typically has a .world extension.

The Gazebo server (gzserver) reads this file to generate and populate a world.

A number of example worlds are shipped with Gazebo. These worlds are located in <install_path>/share/gazebo-<version>/worlds.

Model Files

A model file uses the same SDF format as world files, but should only contain a single <model> ... </model>. The purpose of these files is to facilitate model reuse, and simplify world files. Once a model file is created, it can be included in a world file using the following SDF syntax:

   

    

     

      

     
     

      

       <include>
      
     
    

     

      

     
     

      
  <uri>model://model_file_name</uri>
      
     
    

     

      

     
     

      

       </include>
      
     
   
  

A number of models are provided in the online model database (in previous versions, some example models were shipped with Gazebo). Assuming that you have an Internet connection when running Gazebo, you can insert any model from the database and the necessary content will be downloaded at runtime.

Environment Variables

Gazebo uses a number of environment variables to locate files, and set up communications between the server and clients.

Starting with Gazebo 1.9.0, default values that work for most cases are compiled in. This means you don't need to set any variables.

Here are the variables:

GAZEBO_MODEL_PATH: colon-separated set of directories where Gazebo will search for models

GAZEBO_RESOURCE_PATH: colon-separated set of directories where Gazebo will search for other resources such as world and media files.

GAZEBO_MASTER_URI: URI of the Gazebo master. This specifies the IP and port where the server will be started and tells the clients where to connect to.

GAZEBO_PLUGIN_PATH: colon-separated set of directories where Gazebo will search for the plugin shared libraries at runtime.

GAZEBO_MODEL_DATABASE_URI: URI of the online model database where Gazebo will download models from.

These defaults are also included in a shell script:

source <install_path>/share/gazebo/setup.sh

  

If you want to modify Gazebo's behavior, e.g., by extending the path it searches for models, you should first source the shell script listed above, then modify the variables that it sets.

Gazebo Server

The server is the workhorse of Gazebo. It parses a world description file given on the command line, and then simulates the world using a physics and sensor engine.

The server can be started using the following command. Note that the server does not include any graphics; it's meant to run headless.

gzserver <world_filename>

  

The <world_filename> can be:

1. relative to the current directory,

2. an absolute path, or

3. relative to a path component in GAZEBO_RESOURCE_PATH.

Worlds that are shipped with Gazebo are located in <install_path>/share/gazebo-<version_number>/worlds.

For example, to use the empty.world which is shipped with Gazebo, use the following command

gzserver worlds/empty.world

  

Graphical Client

The graphical client connects to a running gzserver and visualizes the elements. This is also a tool which allows you to modify the running simulation.

The graphical client is run using:

gzclient

  

Server + Graphical Client in one

The gazebo command combines server and client in one executable. Instead of running gzserver worlds/empty.world and then gzclient, you can do this:

gazebo worlds/empty.world

  

Plugins

Plugins provide a simple and convenient mechanism to interface with Gazebo. Plugins can either be loaded on the command line, or specified in a world/model file (see the SDF format). Plugins specified on the command line are loaded first, then plugins specified in the world/model files are loaded. Most plugins are loaded by the server; however, plugins can also be loaded by the graphical client to facilitate custom GUI generation.

Example of loading a plugin on the command line:

gzserver -s <plugin_filename> <world_file>

  

The same mechanism is used by the graphical client:

gzclient -g <plugin_filename>

  

For more information refer to the plugins overview page.

Introduction

Gazebo uses a distributed architecturewith separate libraries for physics simulation,rendering, user interface, communication, and sensor generation.Additionally, gazebo provides two executable programs for running simulations:

• a server gzserver for simulating the physics, rendering, and sensors

• a client gzclient that provides a graphical interface tovisualize and interact with the simulation

The client and server communicate using the gazebo communication library.

Communication Between Processes

The communication library currently uses the open sourceGoogle Protobuf for the message serializationand boost::ASIO for the transport mechanism.It supports the publish/subscribe communication paradigm.For example, a simulated world publishes body pose updates,and sensor generation and GUI will consume these messages to produce output.

This mechanism allows for introspection of a running simulation,and provides a convenient mechanism to control aspectsof Gazebo.

System

Gazebo Master

This is essentially a topic name server.It provides namelookup, and topic management.A single master can handle multiple physics simulations,sensor generators, and GUIs.

Communication Library

• Dependencies: Protobuf and boost::ASIO
• External API:
• Internal API: None
• Advertised Topics: None
• Subscribed Topics: None

This library is used by almost all subsequent libraries.It acts as the communication and transport mechanism for Gazebo.It currently supports only publish/subscribe,but it is possible to useRPCwith minimal effort.

Physics Library

• Dependencies: Dynamics engine (with internal collision detection)
• External API: Provides a simple and generic interface to physics simulation
• Internal API: Defines a fundamental interface to the physics library for 3rd party dynamic engines.

The physics library provides a simple and generic interface tofundamental simulation components, including rigid bodies,collision shapes, and joints for representing articulationconstraints.This interface has been integrated with four open-sourcephysics engines:

• Open Dynamics Engine (ODE)
• Bullet
• Simbody
• Dynamic Animation and Robotics Toolkit (DART)

A model described in theSimulation Description Format (SDF)using XML can be loaded by each of these physics engines.This provides access to different algorithm implementationsand simulation features.

Rendering Library

• Dependencies: OGRE
• External API: Allows for loading, initialization, and scene creation
• Internal API: Store metadata for visualization, call the OGRE API for rendering.

The rendering library uses OGRE to provide a simple interfacefor rendering 3D scenes to both the GUI and sensor libraries.It includes lighting, textures, and sky simulation.It is possible to write plugins for the rendering engine.

Sensor Generation

• Dependencies: Rendering Library, Physics Library
• External API: Provide functionality to initialize and run a set of sensors
• Internal API: TBD

The sensor generation library implements all the various types of sensors,listens to world state updates from a physics simulator andproduces output specified by the instantiated sensors.

GUI

• Dependencies: Rendering Library, Qt
• External API: None
• Internal API: None

The GUI library uses Qt to create graphical widgets for users to interact with the simulation.The user may control the flow of time by pausing or changing time step sizevia GUI widgets.The user may also modify the scene by adding, modifying, or removing models.Additionally there are some tools for visualizing andlogging simulated sensor data.

Plugins

The physics, sensor, and rendering libraries support plugins.These plugins provide users with access to the respective librarieswithout using the communication system.

Capture screenshots

To capture a screenshot of the scene displayed in the Gazebo 3D render window, find and click on the camera icon on the toolbar above the render window.

Screenshot save location

The captured image will be saved to ~/.gazebo/pictures with a timestamped filename.